Electronic Structure And Optical Properties Of Nano-MoS₂ And Its Derivatives

With the development of science and technology, design and manufacturing of miniaturized and multi-functional electronic components has been paid more attention. In contrast to conventional int-egrated circuits, electronic components made of nanomaterial show less power consumption and unique physical and optical properties arising from the quantum confinement. Materials such as graph-ene, Mo S2 is widely considered to be applied to nanoelectronic devices. As a typical transition metal dichalcogenides, MoS2 has strongly bonded layers. Instead of zero band gap of graphene, MoS2 monolayers has a direct band gap of 1.85 eV. The excitons transitions between the maximum of split valence bands and the minimum of the conduction band induce its photoluminescence. The carrier mobility of MOSFETS made of MoS2 can be achieved 200 cm2V-1s-1. What's more, the on-off current ratio can be achieved 108 and standby power is very low. So MoS2 is one of the most popular materials for nest generation nanoelectronic devices. In our study, the electronic structure and optical properties of both few layers MoS2 and MoS2 nanotubes are investigated with first-principles calcula-tions based on Density Functional theory. The content of this thesis is as follows: Chapter 1. A brief introduction for nanostructures,nanomatericals and the research of the photoelectric properties of MoS2 and related materials are given. Chapter 2. The basic prinpicle of optical absorption and Density Functional Theory are introduced. Chapter 3. The electronic structure and optical properties of few-layers MoS2 are investigated. When the polarization direction of the light is perpendiculars to c axis, the location of the absorption peaks in the dielectric function diagram changes little but when the polarization direction of the light is parallel to c axis, spectrum line moves toward higher frequencies. While the charge distribution and the dielectric function diagram of Li-doped MoS2 layers show a great difference, then the physical mechanisms behind is explained. Chapter 4. The thermal stability of ultrathin MoS2 nanotubes and the geometrical structure of these nanotubes which may be stable are investigated. Compared to the thermal stability of MoS2 clusters, it reveals that Mo S2 nanotubes with(4,4) and diameter larger than(5,5) are considered to be the smallest tubes that may exist. Then we further study the band structure and the optical properties. Chapter 5. Summary and prospects are given.